Engines may use various forms of fuel delivery to provide a desired amount of fuel for combustion in each cylinder. One type of fuel delivery uses a port injector for each cylinder to deliver fuel to respective cylinders. Another type of fuel delivery uses a direct injector for each cylinder.
Engines that use more than one type of fuel injection have been proposed. For example, the papers titled “Calculations of Knock Suppression in Highly Turbocharged Gasoline/Ethanol Engines Using Direct Ethanol Injection” and “Direct Injection Ethanol Boosted Gasoline Engine: Biofuel Leveraging for Cost Effective Reduction of Oil Dependence and CO2 Emissions” by Heywood et al. describe engines that use more than one type of fuel injection. Specifically, the Heywood et al. papers describe directly injecting ethanol to improve charge cooling effects, while relying on port injected gasoline for providing the majority of combusted fuel over a drive cycle. The ethanol provides increased charge cooling due to its increased heat of vaporization compared with gasoline, thereby reducing knock limits on boosting and/or compression ratio. Further, water may be included in the mixture. The above approaches purport to improve engine fuel economy and increase utilization of renewable fuels.
The inventors herein have recognized several issues with such an approach. Specifically, engines designed/optimized for gasoline generally may be detonation (“Knock”) limited and tend to use higher heat range spark plugs to avoid fouling under cold start conditions. The heat ranges (i.e. operating temperature ranges) of spark plugs that avoid fouling are generally well below the heat ranges of spark plugs that would lead to preignition of the gasoline, where “preignition” may include flame origination that occurs from a “hot spot” in the combustion chamber before the intended combustion is initiated by the spark plug discharge. Conversely, engines designed for ethanol usage may be preignition limited as the ethanol has a higher “octane” rating (i.e. resistance to detonation), and the higher compression ratios and earlier spark timing used to improve thermal efficiency can lead to higher combustion chamber temperatures which, combined with the ignition characteristics of ethanol, may increase the chance of preignition.
As such, the inventors herein have recognized an approach to address the above competing spark plug requirements. In one example, a system may include a combustion chamber; a delivery system configured to deliver a fuel and a fluid to the combustion chamber; an ignition system including a spark plug configured to deliver a spark to the combustion chamber; and a control system configured to respond to a change in a condition of the ignition system by varying at least one of an amount of the fuel and an amount of the fluid delivered to the combustion chamber to vary a ratio of the fluid and the fuel or spark timing. For example, the condition of the ignition system includes an ionization detected at the spark plug.
In this way, it is possible to utilize conditions of the ignition system, such as via ion sensing, to discriminate between spark plug fouling and preignition conditions. Further, it can be used to adjust one or more engine operating parameters such as the amount of the fluid and fuel delivered to the engine and/or to adjust spark plug and/or cylinder temperature to limit the spark plug fouling and/or preignition conditions. Thus, the occurrence of preignition, spark plug fouling, and misfire may be reduced while using varying amounts of fuel (e.g. gasoline) and a fluid (e.g. ethanol, methanol, water) to reduce knock limitations. Furthermore, by avoiding or reducing conditions where preignition and spark plug fouling occur, the range of fuel formulation delivered to the combustion chamber may be expanded, thereby further improving engine performance and efficiency, under some conditions.